Chopper



April 1954 R. wooos 2,677,027

CHOPPER Filed Aug. 4, 1952 3 TI. lo 9 n l5 I h 26 NH :1 I E 2a\ IF U IN VEN TOR.

LEROY R. WOODS ATTORNEY Patented Apr. 27, 1954 Leroy Rrwoodsg Whittier, Calif; assigno'rto 4 North American Aviation Inck 7 Application August 4, 1952,.Serial No;302,605

8 Claims. 1

This invention relates" to vibratory signal inter rupters, and particularly to a chopper type signal interrupter which is characterized by low noise and'i'n'creased dependability of operation.

Electromagnetic signal interrupters are used current amplifiers which necessitate "the "rapid periodic interruption or an inputsig'nal', theap plic'atioh'of an input signer to a separate circuit such as an A.-C; amplifier, andthe subsequent synchronous rectification of the signal. No'rmally', it is required that an amplifier ofthis" type respondto '1OW"1eve1" signals (if direct 'currentor orvery-rlow frequency; It is important'in's'uch' devices" that chopper operation be substantially noise free and free from the effect of tempera-- ture change, and that the device be constructed for longandtrouble-free operation. Where synchronousrectificationis used it is further essentiallthatthe capacitance between the input and output 1 chopper contacts; and the capacitance from the contacts to'gr'o'und' be a minimum.

It is therefore an object of this invention to providean improved electromagnetic chopper.

It is another object of thisinv'ention' to provide an" electromagnetic chopper which is non-temperature sensitive.

It is" another object of this invention to provide an electromagnetic chopper which operates 'at double'the driving frequency to thereby eliminate error resulting from pickup by an associated amplifier at the driving frequency;

It is another object of this invention to provide an electromagnetic chopper of minimum 'capac-' itance between the signal-carrying elements thereof and ground.

It is anotherobject of this invention to provide an'ele'ctromagnetic chopper which is readily adjustableby' means accessible from the outside thereof:

It'is; another'object'of this invention to provide amelectromagnetic chopper which is characterized byintroducing negligible" electrical noise;

It is another object of this inventionto provide an electromagnetic chopper the period of electricalcontact in which maybe readily adjusted.

Other objects of invention will become apparehtfrointhefollowing description taken in connectionwith the accompanying single figure which is a cutaway viewof the invention.

Referring to the single figure, a tubular frame I carries at one end a flexible reed 2 cantilevered andattached-by a nut 3- Reed 2 carries a crossarm 4 havingplatinum-iridium alloy tips 5 and 6. This alloy is preferably made "of 70 percent plati num and 30 percent iridium. Reed 2 also carries at "itsrend: a mass- 1- of ferromagnetic material whi'ch serves as an actuator for the reed. At the opposite end of frame I and interiorly disposed, cantilever members 8 and 9 are anchored securely in rramel, GLSGhOWIiI' T116 free endSU'fTh'fhbers 8" and 9 maybe 'adjlis't'd' transverselyby" screws I0 and l I threa'ded'into-a portionofframe" l. Members 8' ends are flat, l'eaflike cantilever" beams having holes-"i2 and i3 arrangedto"ae= commodate orossarm '4', as "shOWIi. "Contact men'r:

bers l4 and I5 are positioned outboard"f'rom members 8 and 9, and carry platinum-iridium alloy strips l6 andl'fdispoeed tobecontacted by the ends of crossar'm'a; The ends or-mem= bers M and1'5 restup'on insulatingmeanssuch as jewels I8 and" [9 which are secured to'the outer surfaces of stop members Band '9. Ree'd2 is caused to oscillate b -theinfioenceor -electr6=-' magnet 20' which is disposed adjacent to mass-f1" and off-center fromth'e axisof reed "2. Alter hating current is supplied to 'electromagnet' 20' from any source'- of alternatingcurrent-through contact memberssuch as prongs 21', 22,23, 24, and 25, similar to tube baseprongs. The vertical position of 'electrom'ag'net' 20 and hence, to some extent, theamplitude of motion of reed 2 maybe adjusted by rotation of cam 26 in the lower portion of frame I. Frame I attached to base 2"! to which is also attachedcover' 28 used for shielding purposes. Contaet*members M and" I5 are connected to a pair of contact prongs, as'is frame'l. Preferablmfram I, feed 2, and all othernonelectrical parts of-the device are constructed of some low temperature coefll-- cient of expansion material such as Invar.

In operation; alternating current 'issupplied" shown, so that a signal supplied to one of the contact members is periodically connected to the frame, and this connection is broken; As reed 2 moves'transversely and contact is made'b'etweem platinum-iridium alloy tips 5 or 6 and'pla'tinum iridium alloy strips IE or 11, members 14 and l-5 yield, with the result that they are removed-from contact-with jewels I 8 and icon members 8and 9. Because of the arcuate motion of "strips [tand- H, the amount'of slippage between the contacts on the crossarm and the contact strips is min? imize'd, and "a good electrical connection'is ei fecte'd. The length'of timethat contact is made each cycleis affect'ed'by the adjustment of screws l6 and which adjust the transverse positions of members 8 and 9. The amplitudeofcscillaetion of reed 2 may be adjusted somewhat-"by movingelectromagnet 26 longitudinally"by rota tion of cam 26."

Because frame I is insulated from base member 21 and from cover 28, the frame may be held is insulatingly at a different potential from the cover, and hence from the chassis or other device used to support the chopper. Because of the arrangement of contact members [4 and [5, the capacitance between these members and the frame is minimized. The use of platinum-iridium alloy contact members reduces noise which would otherwise be introduced into the circuit when the contacts are made and broken. Jewels i8 and I9 minimize wear of members M and 15, resulting in a relatively long life of the device without frequent adjustment. It will be noted, too, that the chopping frequency of the device is double the frequency of the driving signal applied to-electromagnet 20.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

I claim:

1. A vibratory signal circuit interrupter for converting signals of low frequency and low potential in the circuit to relatively high frequency without loading the signal source and without introducing appreciable noise comprising an elastic conducting reed, means for vibrating said reed at constant predetermined frequency, a crossarm on said reed oriented parallel to the direction of vibration thereof and a contact on each end thereof, a generally cylindrical frame for supporting said reed at one end thereof having an integral centrally disposed block with an aperture sufficient to allow motion of said reed, a pair of stop members attached to said block yieldable in a direction parallel to the motion of said reed and having openings for accommodating the ends of said crossarm without touching them and jewels secured at a predetermined position on the outer surface of said stop members, a pair of yieldable contact members attached to said block outboard from said stop members said contact members having platinum-iridium alloy contact strips aligned opposite the ends of said crossarm and tips spaced to be normally in contact with the outer surface of said stop members at the location of said jewels but disconnected from said stop members by motion of said reed, and means for adjusting the spacing between said reed and stop members whereby if the signal to be converted is supplied to said contact members said signal is converted to a relatively high frequency without introduction of appreciable noise or distortion.

2. A signal interrupter comprising an elongated generally tubular frame having a plurality of side openings, a first pair of similar cantilever beams attached internally to one end of said frame and extending within said frame toward the other end of said frame, a second pair of similar cantilever beams attached internally to the same end of said frame as said first pair of cantilever beams and extending generally parallelto said first pair of cantilever beams but each disposed outboard from one of said first pair of cantilever beams and each bent at the free end thereof to contact with one of said first pair of cantilever beams, a jewel on each of the ends of said second pair of cantilever beams, said first pair of cantilever beams disposed opposite an elastic reed cantilevered from the other end of said frame and having a symmetrically disposed crossarm arranged to contact said second pair of cantilever beams alternately when said reed is oscillated without touching either of said first pair of cantilever beams, platinum-iridium alloy contact strips on said second pair of cantilever beams positioned to be contacted by said crossarm as said reed is oscillated, and electromagnetic means for oscillating said reed whereby signals supplied to said second pair of cantilever beams are periodically interrupted by contact of said crossarm with one of said second pair of cantilever beams.

3. A device as recited in claim 2 and further comprising means for adjusting the spacing of said first and second pairs of cantilever beams.

4. A device as recited in claim 3 in which said electromagnetic means comprises a mass of ferromagnetic material on the end of said reed and an electromagnet positioned adjacent said mass but displaced from the axis of said reed.

5. A device as recited in claim 2 and further comprising platinum iridium alloy tips on the ends of said crossarm to thereby minimize electrical noise in the resultant signal.

6. A device as recited in claim 2 and further comprising a socket connection for receiving connections to said frame and said second pair of cantilever beams, and a shield over said frame whereby said frame may be held at a different potential from said shield and said socket connector.

7. A device as recited in claim 2 in which said beams, said frame, and said reed are constructed of metal having a low coefficient of temperature expansion to thereby substantially eliminate the effect of temperature on the operation thereof.

8. A signal interrupter comprising an elongated generally tubular frame having a plurality of side openings, a first pair of similar cantilever beams attached internally to one end of said frame and extending within said frame toward the other end of said frame, a second pair of similar cantilever beams attached internally to the same end of said frame as said first pair of cantilever beams and extending generally parallel to said first pair of cantilever beams but each disposed outboard of one of said first pair of cantilever beams and each bent at the free end thereof to contact with one of said first pair of cantilever beams, insulating means on each of the ends of said second pair of cantilever beams, said first pair of cantilever beams disposed opposite an elastic reed cantilevered from the other end of said frame and having a symmetrically disposed crossarm arranged to contact said second pair of cantilever beams alternately when said reed is oscillated without touching either of said first pair of cantilever beams, platinumiridium alloy contact strips on said second pair of cantilever beams positioned to be contacted by said crossarm as said reed is oscillated, and electromagnetic means for oscillating said reed whereby signals applied to said second pair of.

cantilever beams are periodically interrupted by contact of said crossarm with one of said second pair of cantilever beams.

References Cited in the file of this patent 

